2.11 In vivo wound closure assay
C57BL/6 male mice were anesthetized by intraperitoneal injection of 4% chloral hydrate. The skin hair on the backs of mice was removed using a shaving machine and depilatory creams. Alcohol was used to rinse the skin, and silicone rings with an internal diameter of 8 mm and thickness of 0.5 mm were stitched on the skin. Two full-thickness wounds per mice were made on the dorsal skin with surgical scissors. After surgery, the wounds were treated with 10 μL FGF2 or PEG-FGF2 conjugates (10 μg·ml-1, produced by Wenzhou Medical University gene engineering laboratory) or PBS once a day. Digital photographs of the wound area were taken on days 0, 3, 5, and 7 and the wound areas were measured using ImageJ software. The ratio of wound healing was defined as the ratio of (the original wound area - the wound area on the collected day) to the original wound area. Skin wound samples were collected 7 days after injury and fixed in 4% paraformaldehyde for histological and immunofluorescence analyses.